Metasurface: Changing polarization from linear to circular for airborne antenna

Abstract

To implement the circular polarization antenna on the airborne electronic platform, a new technique of polarization change is investigated in this paper. A metasurface structure consisting of a 5 × 5 array has been designed. Each unit of the metasurface structure is a stack circular ring, and two orthogonal dipoles in a ring can convert the linear polarization wave into circular one. An ultra-wideband (UWB) antenna is designed combining with the metasurface structure. To filter some interference signals from special frequency bands such as WLAN and WiMAX, dual notched-bands have been designed on the UWB antenna. Therefore, dual circular polarization radiation character at two bands of 4 GHz–7.9 GHz and 8.1 GHz−12.4 GHz is achieved. The antenna with metasurface is operated at 2.6 GHz–13.6 GHz excepting for two notched-bands of 3.15 GHz–4.3 GHz and 5.5 GHz–5.75 GHz. Fabricated sample has been verified by experiment, and the results indicate that the design is available.

Introduction

Nowadays, for the airborne electronic system, anti-interference ability and wider frequency band are very required. The antenna is an important device for transmitting and receiving wireless signal, and plays an irreplaceable role in the airborne communication system. In order to obtain the good performance of airborne communication system, on the one hand, the polarization of antenna is controlled. Because multiple polarizations of antenna will improve the channel capacity [1], [2], and circular polarization wave has obvious advantages in anti-interference [3], [4]. The communication quality will be improved if signal is transmitted by circular polarization wave [5], [6]. Simultaneously, circular polarization wave can be received by any linear polarization antenna. Linear polarization wave can also be received by any circular polarization antenna [7]. This feature reduces the difficulty of deployment during antenna installation. Hence, the dual circular polarizations antenna is much more required.

On the other hand, the operating bandwidth of antenna is an important affecting factor on performance of airborne communication system. The channel capacity is proportional to operating bandwidth of antenna by Shannon's theorem, so the ultra-wideband (UWB) antenna is a good choice for airborne communication system. In ultra-wideband application, the parallel-plate etched slot antenna of high efficiency possesses great advantages. In [8], [9], some good performances of post wall-based parallel-plate slot antenna have been contained. Moreover, monopole ultra-wideband patch antennas are commonly applied in ultra-wideband communi- cation system because they are cheap and low loss [10], [11]. Though, the ultra-wideband property is implemented by the above two types antenna, dual circular polarization can’t be implemented at the same time.

Most UWB antennas radiate linear polarization wave [12], [13], [14]. But the linear polarization wave is easily affected by multipath interference, rain, snow, and fog in propagation process. The circular polarization character is difficult to implement from ultra-wideband antenna. In general, the circular polarization is achieved by two orthogonal linear polarization waves or 90° phase different feed [15], [16]. As a result, many researchers dedicate to research of circular polarization antenna. A dual circular polarization antenna with ring slot has been designed for K-band downlink and uplink, by applying sequential rotation technique [17]. A dual circular polarization antenna has been designed to operate on Beidou navigation satellite system (1.59 GHz–1.63 GHz and 2.39 GHz–2.57 GHz), whose circular polarization is implemented through applying method that invert-L and perturbation are inserted in radiation patch [18]. A circular annular ring patch antenna with circular polarization is designed in [19] whose operating band is 1.92 GHz–2.025 GHz. Although circular polarization antennas has been achieved by using the methods above, the antenna is still limited in a narrow operating bandwidth. If the existed antenna is transformed to circular polarization, antenna structure must be improved furtherly.

Recent years, with the development of microwave techniques, metasurface, an artificial electromagnetic material, is considered to convert the linear polarization incident waves into circular polarization reflected waves [20], [21], [22], and it can improve the performance of antenna in terms of axial ratio bandwidth and axial ratio bandwidth [23]. Simultaneously, the structure of the metasurface consisting of 4 × 4 rectangle loops is designed with a diagonal microstrip [24]. After that, a 3 × 3 rectangle with slots metasurface structure is also designed [25]. Nevertheless, both techniques can convert the linear polarization wave into circular polarization wave, the above circular polarization conversion is single one. This must be improved in order to meet dual circular polarization requirement.

In this approach, a circular polarization technique has been developed. Use of metasurface structure, a 5 × 5 array is designed to implement the conversion of circular polarization from learner linear one. The element of metasurface is wheel-shaped with two orthogonal dipoles and four quarter circular rings. The dual notched-bands UWB is combined with metasurface. Then, dual circular polarizations are implemented at dual wide-bands. Fabricated sample has been verified the design.

The rest parts of this paper are organized as follows. By using the high frequency simulation software (HFSS), a wheel-shaped reflective unit and 5 × 5 metasurface structure is designed in Section 2. The 5 × 5 metasurface structure is verified by a dual notched-bands ultra-wideband antenna in Section 3, which can convert linear polarization incident waves into left-hand and right-hand circular polarization waves. Then fabricated samples of designed above have been tested, and experiment results are discussed in Section 4. Finally, conclusions on this approach are given at last Section.